Unfortunately, big pharma has been running Vitamin C down for years. The Linus Pauling Foundation, started after LP first emphasized the importance of high dose Vitamin C in treating a number of illnesses, has been forced to be very careful about anything it says about the value of Vitamin C. Dr. Robert Cathcart has written in great detail about the uses of high Vitamin C in successfully treating a number of major illnesses. It seems that for both Vitamins C and D, there is a big difference between taking enough to prevent scurvy or bone loss, and enough to have an optimum level of that vitamin.
Dr. Cathcart recommends that everyone in normal health should take 4 grams of Vitamin C a day, in divided doses. I have taken from 4 to 7 grams a day for 50 years. At 83 years old, it has done me nothing but good for my several allergies (house dust, mold, and cigarette smoke). I once gave a woman stung by 3 yellow jackets in the neck 50 grams of C over 8 hours (she had forgotten her bee sting kit for this wilderness trip). The first 10 grams crushed and mixed in a glass of water opened her swollen throat, and eyes in 20 minutes.
With regard to Vitamin D, science is now coming to the conclusion the level of Vitamin D (above 20 ng/mL blood level) which is good for bone health, may not be enough for optimum immune health. In fact Kaiser Permanente gives the OPTIMUM RANGE for Vitamin D blood levels as 50 to 80 ng/mL. The link below is a Covid study which used over 200 people for a test of the original Dr. Zelenko 3 part Covid treatment protocol, plus Vitamin D, and either using or not using IV (intravenouse) Vitamin C. They were testing whether using the Vitamin C would improve hospitalization outcomes. While they did find the IV Vitamin C definitely shortened hospital stays, an even more exciting find concerned Vitamin D. They had done various blood tests before the experimental study began. After the experiment was over they went back to these preliminary tests and discovered NO test subject had an OPTIMUM Vitamin D level. This study used above 30 ng/mL as their OPTIMUM, far lower than the Kaiser Permanente 50 to 80 ng/ml level. My conclusion is that if you want to stay out of hospitals for illness, get tested, and find out how much Vitamin D3 you need to reach and maintain an OPTIMUM Vitamin D level. [NOTE: The foreign study below uses nmol/L (nanomols/liter) rather than the US ng/mL (nanograms/milliliter). You need to divide the foreign measures by 2.5 to determine the US figures. Thus 75 nmol/mL becomes 30 ng/mL when divided by 2.5.]
You may have difficulty finding a doctor who knows how much Vitamin D3 will bring you up to the OPTIMUM level. I am a 140 lb. woman, and after taking 2000IU to 5000IU of Vitamin D3 since summer 2020 tested at 66 ng/mL at KP this past Dec. I used less with ample sun exposure and in summer, and more when mostly indoors and in winter. A 235 lb. man I know was taking 5000IU, but this winter his doctor said to take 10,000IU a day. Dark skinned people have difficulty absorbing vitamin D formed in their skin by the sun. A large black woman I met said her doctor told her years ago to take 10,000IU daily. She is tested annually. [All 3 people live in the mid-Atlantic area.] So, good luck finding the ideal amount of Vitamin D3 to keep you out of hospitals.
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This is very important